Haze Across Northern India

A pale band of haze hangs along the front of the Himalaya Mountains in Nepal, India, and Bangladesh in this photo-like image, taken on February 5, 2006, by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite. One source of the haze is the fires that burn throughout the region. The fires, marked in red, were probably deliberately set for agricultural purposes. Another source of the haze is the cities of northern India, the grey dots that stand out against the green agricultural areas in the plain to the south of the mountains. The largest of the cities is New Delhi, the capital of India.
It is common to see dense haze in northern India, Nepal, and Bangladesh during the winter. The haze lingers near the base of the mountains because of a temperature inversion. In normal conditions, the air near the ground is warmer than the air above it. Warm air rises and carries with it pollution from fires or cities. The pollution disperses when it is mixed with cooler air high above the ground. During the Himalayan winter, cold air rushes down the mountains onto the plain. This makes the air near the ground cooler than the air above it, essentially trapping a pocket of cold air over the plain. Smoke from fires and regular pollution from cities is also trapped in the pocket of cold air and don’t disperse as they would under normal conditions. As a result, haze builds until the inversion lifts. The haze shown in this image had been accumulating for several days, and is visible in several other MODIS images, including one acquired on February 1, 2006.
Credit: Jeff Schmaltz, MODIS Rapid Response Team, NASA/GSFC